This invention relates generally to flexible containers for transporting and storing goods and, more particularly, to such flexible containers which are constructed from a tubular blank formed so as to include a shell, a bottom and a filling aperture, the container being liftable by its upper end and wherein pleats are formed in the container shell having lower parts which are folded into the plane of the container bottom.
A first type of flexible transport and storage container for bulk goods is known and is disclosed in Finnish patent application No. 771681 corresponding to U.S. Pat. No. 4,136,723 to Skaadel et al. A container of this type is preferably provided with an inner bag substantially formed of a single piece of tight material having lifting loops in its upper portion and a filling aperture in a central portion. The bottom portion of the container includes at least four flaps provided in respective pairs of equal size flaps and which constitute linear extensions of the container shell, the flaps of each pair being joined at the lower margin so as to form juncture lines which intersect at a single point. Similar bags of this type are also disclosed in CH-patent No. 362,970 and in German Publicizing Print No. 1,126,795. A drawback inherent in large-size bags of this first prior art type is that the bottom of the bag cannot with stand the high stresses to which the central region of the bag bottom is subjected when the bag is filled with bulk goods. This inability to withstand high stresses is due to the fact that the juncture lines provided in the bag bottom intersect at the central point of the bag when the highest peak stresses occur. The peak stresses occur in the central region of the bag bottom as a result of the fact that when filled with bulk goods, the bottom portion of the large-size bag tends to assume a rounded shape.
A second type of prior art flexible container for transporting and storing bulk goods is disclosed in Finnish patent application No. 793,030. In a container of this prior art type, the bottom is constructed of strip-like parts which are joined by connecting seams which are disposed to extend at a substantial distance from the central area of the bag bottom. A container bottom of this type is capable of reliably withstanding all stresses which may be imposed on the container bottom in normal practice since no connecting seams are disposed in the central region of the container bottom which would tend to reduce the strength thereof. This known design for a container bottom may be utilized equally as well in containers provided with lifting loops in their upper portion as well as in containers which are not provided with such lifting loops. Such containers which are not provided with lifting loops, i.e. so-called open bags, are sealed at their filling apertures and may be lifted, for example, utilizing an appropriate lifting hook.
Containers of the second prior art type discussed above have the drawback that the relatively complex structure of the container bottom prevents the manufacture of such containers in an automated fashion or at least makes such automation exceedingly difficult and costly to accomplish. Moreover, several separate manufacturing steps are required to construct containers of this second prior art type, namely, cutting the bottom strips and the affixation of the same. Such drawbacks result in relatively high production costs.
A third type of prior art large-size bag is also known, namely, the so-called pleated large-size bag. In this construction, pleats are formed in the shell of the bag having lower parts which are folded into the plane of the container bottom. In such prior art pleated large-size bags, the pleats are open, whereby the lower side of the pleat is free while the upper side of the pleat becomes taut when stress is applied on the bag. The peak stress is particularly directed on the so-called apex of the pleat, which is constituted by the inside apex point of the large-size bag. Prior art containers of this type have the drawback that the same are frequently ruptured due to the stress conditions arising at the pleat apex, the rupture usually initiating at the pleat apex.